Interpretive Summary: Ricinoleate, a hydroxy fatty acid, in castor oil has many industrial uses such as the manufacture of biodegradable plastics, plasticizers, lubricants, cosmetics, paints and surfactants. Castor is the only commercial source of ricinoleate. Lesquerolate, a hydroxy fatty acid in lesquerella oil, also can be used in industry similar to those of ricinoleate. Tetraacylglycerols have different physical properties from those of triacylglycerols and can be used in industry for different physical properties such as viscosity and pour point improvers for lubricants. We have identified 13 tetraacylglycerols containing lesquerolate in lesquerella oil. The contents of these tetraacylglycerols can be increased in the future for industrial uses. The biosynthetic precursors of these tetraacylglycerols were proposed.

Technical Abstract:
Tetraacylglycerol (an acylglycerol estolide) contains an acyl chain attached to the hydroxyl group of another acyl chain attached to the glycerol backbone. Lequerolic acid (Ls, OH1420:111) is the main fatty acid in lequerella oil and can be used in industry. We have used electrospray ionization mass spectrometry of the lithium adducts of acylglycerols in the HPLC fractions of the seed oil of Lesquerella fendleri to identify thirteen tetraacylglycerols. They were LsLsLsLn, LsLsLsL, LsLs-OH20:2-O, LsLsLsO, LsLsLnLn, LsLsLLn, LsLsOLn, LsLsLL, LsLsOL, LsLsOP, LsLsOO, LsLsLS and LsLsOS. The OH20:2 was auricolic acid (OH1420:211,17). For the four tetraacylglycerols containing one normal fatty acid (non-hydroxy fatty acid), LsLsLsLn, LsLsLsL, LsLs-OH20:2-O and LsLsLsO, the normal fatty acids were all directly attached to the glycerol backbone, not to the hydroxyl group of fatty acids. We propose that the biosynthetic precursors (triacylglycerol acyltransferase) of these four tetraacylglycerols were LsLsLn, LsLsL, LsLsO (Ls-OH20:2-O) and LsLsO individually. LsLsO and Ls-OH20:2-O were equally active as the biosynthetic precursors for LsLs-OH20:2-O. For LsLsLS, linoleate were all attached to the glycerol backbone and LsLsL was proposed to be the biosynthetic precursor. For LsLsOS, stearate were all attached to the glycerol backbone and LsLsS was proposed to be the biosynthetic precursor. For the other seven tetraacylglycerols containing two normal fatty acids, LsLsAB, the biosynthetic precursors could be both LsLsA and LsLsB.